Aer Lingus workers' unions clashed over commitments from the airline's chief executive Stephen Kavanagh on jobs as the Government agreed to sell its share in the company.

Mr Kavanagh, who is set for a €720,000 windfall from the sale, offered stronger guarantees on jobs late on Wednesday night, when his first offer was opposed by unions.

In a letter to Employment Minister Gerald Nash, the Aer Lingus boss committed to entering a collective agreement on compulsory redundancies and outsourcing if efficiencies can be achieved in the company. He also pledged to include more staff members in existing registered employment agreements.

Siptu president Jack O'Connor welcomed the improved offer, which he said was "significant".

Mr O'Connor said his union already has an agreement with the company on achieving efficiencies and expected this would not be a problem for his workers.

However, he said the union was of the understanding that the commitments in Mr Kavanagh's letter were binding - and if they were not honoured, the Labour Party would have to answer.

"Our understanding would be that the sale would be conditional on the agreements that the Government negotiated with Aer Lingus and IAG and the undertakings that were given in the context of that agreement," Mr O'Connor said.

"In the event that it is not honoured, we will be going back to the Government, and the Labour Party in particular, because they are people who extracted this commitment.

"We will say the commitments you gave are not being honoured, and you can't let this sale go ahead unless they are being honoured."

The Impact trade union, which represents 2,000 Aer Lingus staff, said the Dáil vote on the sale would "elevate concerns" of possible redundancies when the takeover was completed.

The union's national secretary Matt Staunton said Mr Kavanagh's commitments were conditional on staff providing further efficiencies.

"The employer will look to extract these from Aer Lingus staff. In other words, the employer is saying to staff that they have a choice between their job or a further erosion of their terms and conditions of employment," Mr Staunton said.

"Too many questions remain about what management will look to extract from its workforce when the inevitable restructuring phase commences under new ownership."

Transport Minister Paschal Donohoe acknowledged that the commitments on outsourcing and redundancies from Aer Lingus were not legally binding.But he said legislation of registered employment agreements would be enacted shortly.

Meanwhile, the Aer Lingus Group welcomed the Dáil vote on the sale of the company.

The group's chairman Colm Barrington described the deal as "compelling" and said shareholders would receive an "attractive return" from the sale.

He said Aer Lingus would reap the commercial and strategic benefits of being part of a multinational airline company.

"This access to greater global scale will accelerate growth across our network, enhance Ireland's position as a natural gateway connecting Europe and North America, give Irish tourism access to major traffic flows and customer loyalty programmes and provide better access for business interests and to cargo flows," he said.